Let

Now putting,

Ax²+(Bx + C)(3x+8) = 5x+8

Putting 3x+8=0,

By equating the coefficient of x² and constant term,

A+3B=0

8C=8

C=1

From equation (1), we get,

Putting x+2=0,

X=-2

A(-4)²+B(0)+C(0)=-6+1=-5